1. Field of the Invention
The present invention generally relates to a plasma monitoring method that can be applied to a semiconductor production process and other production processes using plasma, and more particularly to a plasma monitoring method for measuring in-situ a resistance of a side wall of a pattern such as a contact hole side wall and a current flowing in the side wall.
2. Description of the Related Art
Plasma monitoring methods for monitoring a wafer that is processed in a plasma apparatus are described for example in Japanese Patent Application Kokai (Laid-Open) No. 2003-282546 and Japanese Patent Application Kokai No. 2005-236199.
Japanese Patent Application Kokai No. 2003-282546 and No. 2005-236199 point out that serious problems such as shape abnormality and/or etching stop caused by an electron blocking (or electron shielding) effect in a plasma process (e.g., dry etching) are encountered as the circuit pattern of a semiconductor device is miniaturized.
The electron blocking effect is described briefly. Electrons (negative electric charge) and positive ions fall on a wafer surface from plasma when plasma treatment is conducted on the wafer placed on a stage inside a plasma chamber. The positive ions fall on the wafer surface almost perpendicularly, but the electrons do not fall perpendicularly. As a result, the positive ions reach a deep bottom of contact holes formed in the wafer and are accumulated therein, whereas the electrons collide with the inner walls (side walls) of contact holes and do not reach the contact hole bottom. The difficulty of the electrons reaching the contact hole bottom due to the incident angle of the electrons is called the electron blocking (or electron shielding) effect. The electron blocking effect creates a difference in the amount of electric charge between the wafer surface and the contact hole bottom, and a difference in electric potential between the contact hole top (upper end) and the contact hole bottom. Accordingly, the etching stop and/or shape abnormality can occur.
In order to resolve these problems, a method has been suggested and studied by which plasma process conditions are decided such that a deposition film with a comparatively low resistance is formed on the side wall of a contact hole and the electrons accumulated on or near the upper end of the contact hole move down along the side wall and cancel the positive electric charge at the contact hole bottom. This will relax the electron blocking effect.
The deposition film is an etching reaction product that is provided on the side wall of the contact hole as a result of chemical reaction between the film to be etched and radicals emitted from plasma during contact etching. The formation of such deposition film on the contact hole side wall is well known in the art. The resistance rate of the deposition film has been reported to change depending on the plasma process conditions (for example, type of gas and applied power) during contact hole etching.
Various researches have been conducted by way of simulation of contact hole etching or the like to reproduce complex phenomena taking place on the side wall of contact hole. For the results calculated by simulation to match the results obtained in the actual etching process, it is desirable that various parameters included in the simulation (e.g., plasma temperature, plasma density, pressure inside the plasma chamber, potential inside the contact hole, and electric current flowing in the side wall of the contact hole) be close to actual values, and the actually measured values be used for such parameters.
For example, the inventors of the present application have disclosed in Japanese Patent Application Kokai 2009-59880 published on Mar. 19, 2009 (Patent Application No. 2007-225677 filed on Aug. 31, 2007) a method for measuring in-situ an electric potential inside a contact hole. The measured electric potential is used as one of the above-mentioned parameters for the simulation. However, a resistance or electric current value of the side wall of the contact hole cannot be measured in-situ by this method.